1. Field of the Invention
The present invention relates to a magnetic recording apparatus equipped with a magnetic head and a magnetic recording medium. Particularly, it relates to a magnetic recording apparatus that is used in low atmospheric temperatures such as below 0° C., and a method of controlling the apparatus.
2. Background Art
In recent years, magnetic recording apparatuses such as magnetic disc drives are being increasingly used as the sole storage unit for information equipment, in addition to their use as external storage units for computers, because of their superiority in terms of per unit information cost. The demand for such magnetic recording apparatuses as storage units in portable information devices or car navigation systems, for example, is particularly increasing, resulting in significantly increased ranges of temperatures in which they are used. Accordingly, there is an increasing demand for magnetic disc devices capable of stable recording and reproduction operations in wide temperature ranges.
A magnetic disc apparatus includes a magnetic recording disc that has a plurality of concentric recording tracks in which servo areas and data areas are alternately arranged circumferentially. The apparatus also includes a positioning mechanism on which a magnetic head for recording or reproducing data is supported. The apparatus is connected to a host device. Upon reception of a command for recording or reproduction of data from the host device, the positioning mechanism transports the magnetic head to a track with a data area where data should be recorded or reproduced, in accordance with servo information that is recorded in the servo areas in advance.
In the case of recording, a recording element in the magnetic head produces a magnetic field by which a target data area on the recording medium is magnetized such that the direction of magnetization is changed alternately, thereby recording information therein. In the case of reproduction, the magnetic field existing on the medium surface due to the magnetization in the recording medium is detected by a read element including a giant magneto resistive element, for example. Changes in the magnetic field are then converted into digital information to read the recorded information. The magnetic head is mounted on a head slider that travels above and relative to the disc surface with a required flying height ensured by the dynamic pressure of airflow created between the head and the disc as it rotates.
If the flying height is too large, the distance between the magnetic head and the recording medium increases, so that the recording element cannot apply sufficient magnetic field to the recording medium. Too much distance would also make it difficult for the read element to detect the recorded field near the surface of the medium. An excessive flying height thus significantly impairs the recording/reproduction performance. On the other hand, if the flying height is too small, dust in the device or bumps on the disc surface might contact the magnetic head and destroy the head elements or the disc by friction. To prevent this, the air bearing surface (ABS) of the head slider is provided with irregularities so that the head slider can be floated by just the right amount by hydrodynamic effects. Thus, the head slider can travel above and relative to the disc with a uniform air pressure, uniform relative speed, and uniform flying height.
The metal and insulator materials that compose the magnetic head expand and contract depending on the ambient temperatures. Particularly in low atmospheric temperatures, these materials contract and so the tip of the recording element retracts from the ABS of the head slider. As a result, the distance between the medium surface and the recording element increases even when the slider floating amount is constant, and the recording performance deteriorates. During recording, the materials expand due to heat generated by the application of current to an excitation coil in the recording element, so that the distance between the medium surface and the recording element gradually decreases. This leads to the problem of errors caused by recording performance deterioration upon start of recording operation, particularly in low atmospheric temperatures such as below 0° C.
As a technique for overcoming the recording performance deterioration in low atmospheric temperatures, JP Patent Publication (Kokai) No. 5-258215 discloses an invention in which recording current is increased in low atmospheric temperatures so as to increase the recording field intensity and thus enhance the recording performance. However, merely increasing the recording current has the problem that increasing the recording current results in saturation of the magnetic poles of the recording element and cannot increase the recording field, thus failing to improve the recording performance.